It depends, but usually the manga is longer so I read that second(:

I believe in knowing the original storyline first.

Actually it depends on what I encounter first like with Meitantei Conan I encountered it's anime first then I saw the manga and wanted to read it while with some series I wanted to see what the manga was like before watching the anime like I did with Ouran so it virtually depends.

Usually I find out about the anime first, once I finish it, I'll usually read the manga afterwards. But sometimes if I want to know what its like/ how good it is, I'll check out the manga first.
But if I read the manga first, then watch the anime I'm usually disappointed with the anime.

I think the anime is kind of like a promo for the manga ^^

depends on the manga or anime...

I always read the manga first, it's kind of like reading the book before you watch the film for me.

The manga is the source material. (Almost always)

Well, I have seen some anime adaptations of the original mangas before I read the mangas. For example, I have watched the anime adaptation of Card Captor Sakura first before I read the original manga version to see the differences between these two versions. Please note that not all mangas came before the anime versions because some of these mangas are manga adaptations of some animes like The Electric Tale of Pikachu is a manga adaptation of the Pokemon anime that take place in an alternate universe of the anime.

generally i only read manga that don't have an anime, since if it does, i'll watch the anime instead.
if a manga to an anime i really like continued from the series and i wanted more of it, i would read the manga from where the anime left off in most cases, rather than reading it from the start